OneTool

Tire Size Speedometer Calculator

See how a size change skews speed and mileage readings.

Same units as your speedometer (mph or km/h) — used only for the actual-speed example.

Overall diameter
24.97″ → 25.72″ (+2.98%)
Revolutions per mile
807.6 → 784.2 (-2.89%)
Speedometer / odometer effect
Diameter change of +2.98% means actual speed and distance are about 1.0298× indicated. Larger tires typically make the speedometer under-read (you’re going faster than shown) and the odometer under-count miles — relevant for speed limits, lease/warranty mileage, and service intervals.
At indicated 60, approximate actual speed ≈ 61.8

What is this tool?

Your speedometer and odometer assume a specific tire circumference. Switching sizes changes nominal overall diameter and revolutions per mile, so indicated speed and recorded mileage can drift from reality — important for speed limits, lease/warranty mileage, and service intervals. Math uses the size-code diameter formula; actual tires differ by brand and measured diameter.

How to use it

  1. Enter the original factory (or current) tire size in standard notation.
  2. Enter the new tire size.
  3. Optionally enter an indicated speed to see approximate actual speed.

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